The publications and other materials used herein to illuminate the background of the invention, and in particular, cases to provide additional details respecting the practice, are incorporated by reference.
Knots, i.e., the branch stubs encased in the tree stem, of Picea abies and Pinus sylvestris contain exceptionally large amounts of bioactive phenolic compounds (1, 2). The amount of extractable phenolic compounds in P. abies knot heartwood, or knotwood for short, can be close to 30% (w/w) but is on average around 15% (w/w) (1). The amount of phenolic compounds in the knotwood is usually 50-100 times that in the stemwood. In P. sylvestris knotwood the amount of extractable phenolic compounds can be as large as 10%, which is several times more than in the stemwood (2). Salix caprea knotwood has also been shown to contain 2-10 times the amount of phenolic compounds found in the stemwood (3). In recent research at our laboratory we have found that knotwood of several other wood species, both softwood and hardwood species, follow the same pattern.
Tree materials such as heartwood, foliage, phloem, bark, and cork of several species have been found to be sources of natural phenolic antioxidants, also including tannins (4-8). However, the extract yield obtained from such materials is low and the extracts usually contain a large variety of different phenolic and non-phenolic compounds, both as glycosides and as free aglycones. The degree of glycosylation affects the antioxidant properties of phenolic compounds. For example, the antioxidant activity was found to be lower for quercetin and myricetin glycosides than for their corresponding aglycones (9). The hydrophilic compounds in softwood knots contain mainly free aglycones of lignans, oligolignans, stilbenes, and flavonoids (1, 2, 10). One or a few phenolic compounds dominate in the knotwood extracts of most softwood species. For example, more than half of the hydrophilic extractives of P. abies knotwood are lignans, the rest being mainly oligolignans, while the two isomers of hydroxymatairesinol constitute over 70% of the lignans (1, 10). Hydroxymatairesinol, extracted and purified from P. abies knotwood, has been found to be a very strong antioxidant in vitro (11).
It is possible to separate most of the knotwood from the over-sized chip fraction in a pulp mill (12). This could be done in order to utilize the extractives found in the knotwood and, at the same time, increase the pulp quality, since wood knots are detrimental during pulping and papermaking. The phenolic compounds could be extracted (13) and, if necessary, purified by chromatographic methods.
Certain phenolic compounds have earlier been suggested for use as antioxidative agents for use in therapy or in food additives. As example can be mentioned the lignan hydroxymatairesinol, the antioxidative use of which is disclosed in WO 00/59946. Also other lignans such as matairesinol have been suggested as antioxidants for medical or cosmetic use.
According to our knowledge, knotwood extracts or fractions thereof have not earlier been suggested as antioxidative agents. Moreover, single lignans or other phenolic compounds, or juvabiones, have not earlier been suggested for use as antioxidants for technical purposes.